In integrated circuit manufacturing, wire bonding is a well proven method used to connect a semiconductor die having electrical circuitry to a pin on a component package. It is also becoming increasingly common to use copper metal interconnects. However, wire bonding directly to copper is not feasible using existing production assembly equipments due to the instability of the native copper oxide at wire bonding temperatures (typically greater than 130 degrees to 170 degrees Celsius).
One solution available today is the use of an aluminum capping layer which is used over the copper bond pads such that the wire bonds are bonding to the aluminum rather than the copper. However, adding an aluminum capping layer increases processing costs. Furthermore, the use of an aluminum capping layer also requires the use of a barrier layer and/or a glue layer between the aluminum capping layer and the copper bond pads which further increases processing costs. Also, an aluminum to gold wire bond typically has reduced mechanical strength as compared to a copper to gold bond.
Another solution available today is the use of a ceramic capping layer which is used over the copper bond pads. The wire bonds must therefore break through the ceramic capping layer via thermosonic energy provided by wire bonders to achieve connection to the copper bond pads. In this solution, the ceramic capping layer is blanket deposited over the entire wafer. However, in order for the wire bonds to be able to break through the ceramic capping layer, the capping layer must be very thin. However, it is difficult to maintain acceptable uniformity when blanket depositing a thin layer thus resulting in reduced assembly yield. Furthermore, the need for a blanket deposit also increases processing costs.
Therefore, a need exists for an improved integrated circuit die having a copper contact which has improved reliability and thermal resistance, while reducing processing costs and increasing assembly yield.
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of the embodiments of the present invention.